The present invention is directed to a printing process that enables simultaneous printing of fixed data (information that remains the same for every document in a series of printed documents) and variable data (information that differs from document to document in a series of printed documents). More specifically, the present invention is directed to a xeroprinting process employing a migration imaging member that enables simultaneous printing of fixed data and variable data. One embodiment of the present invention is directed to an imaging process for simultaneous printing of fixed and variable data which comprises, in the order stated, (1) providing a migration imaging member comprising a substrate, a softenable layer comprising a softenable material and migration marking material contained at or near the surface of the softenable layer, and a charge transport material capable of transporting charges of one polarity; (2) uniformly charging the imaging member; (3) exposing the charged imaging member to activating radiation in an imagewise pattern corresponding to the fixed data, thereby forming an electrostatic latent image on the imaging member; (4) thereafter causing the softenable material to soften by the application of heat, thereby enabling the migration marking material exposed to radiation to migrate through the softenable material toward the substrate in an imagewise pattern corresponding to the fixed data; (5) uniformly charging the imaging member to the same polarity as the polarity of the charges that the charge transport material in the softenable layer is capable of transporting; (6) exposing the charged imaging member to activating radiation in an imagewise pattern corresponding to the variable data, thereby creating an electrostatic latent image on the imaging member corresponding to the variable data in areas of the imaging member wherein the migration marking material has not migrated; (7) uniformly charging the imaging member to the polarity opposite to the polarity of the charges that the charge transport material in the softenable layer is capable of transporting; (8) uniformly exposing the charged member to activating radiation, thereby forming an electrostatic latent image corresponding to both the fixed data and the variable data; (9) developing the electrostatic latent image; and (10) transferring the developed image to a receiver sheet.
Simultaneous printing of fixed data and variable data is often a requirement in many printing applications. Examples of documents containing both fixed and variable data include personalized direct mailing documents, business forms, personalized checks, bank notes, and the like. The documents frequently are characterized by two features. First, the fixed data frequently consist of complicated high resolution images, such as pictures on a bank note, while the variable data typically consist of low resolution text, such as the serial number on a bank note. Second, the amount of variable data in the document typically is much smaller than the amount of fixed data in the document.
In the art of printing/duplicating, various techniques have been developed for preparing masters for subsequent use in printing processes. For example, lithographic or offset printing is a well known and established printing process. In general, lithography is a method of printing from a printing plate which depends upon different properties of the imaged and non-imaged areas for printability. In conventional lithography, a lithographic intermediate is first prepared on silver halide film from the original; the printing plate is then contact exposed by intense UV light through the intermediate. UV exposure causes the exposed area of the printing plate to become hydrophobic; the non-exposed area is washed away by chemical treatment and becomes hydrophilic. Printing ink is then applied to the printing plate and the ink image is transferred to an offset roller where the actual printing takes place. Although lithographic printing provides high quality prints and high printing speed, the processes require the use of expensive intermediate films and printing plates. Additionally, considerable cost and time are consumed in their preparation, often requiring highly skilled labor and strict control measures. A further disadvantage is the time consuming process and difficulty in setting up the printing press to achieve the proper water to ink balance required to produce the desired results during the printing process. This results in further increased cost and delay time in obtaining the first acceptable print.
The above mentioned problems become especially severe in the manufacture of high quality color prints when several color separation images must be superimposed on the same receiving medium. Because of the high cost and complexities associated with the preparations of expensive printing plates and press runs, color proofing is employed to form representative interim prints (called proofs) from color separation components to allow the end user to determine whether the finished prints faithfully reproduce the desired results. As is often the case, the separation components can require repeated alteration to satisfy the end user. Only when the end user is satisfied with the results, a printing plate associated with each separation component is prepared and ultimately employed in the press run. An example of a color proofing system is the CROMALIN system, introduced by E. I. duPont de Nemours & Company in 1972 and widely used in the printing industry, and consisting of a light sensitive tacky photopolymer layer laminated to paper. The photopolymer layer is contact exposed through a color separation component under a UV source. The exposed areas polymerize and lose their tackiness, while the non-exposed areas remain tacky. Toners are then applied and adhere to the tacky areas. Since very different processes are employed in proofing and press runs, the proofs at best can only simulate the press sheets. Additionally, preparation of the color proofs is a time consuming process, and can require about 30 minutes per proof.
Xerographic printing is another well known printing technique. In conventional xerographic printing, an electrostatic image is first produced, either by lens coupled exposure to visible light or by laser scanning, on a conventional photoreceptor; the electrostatic image is then toned, followed by transfer of the toner image to a receiving medium. While this printing process offers the advantages of ease of operation and printing stability and requires less skilled involvement and labor cost, the combined requirements of high quality and high printing speed needed in commercial printing cannot be met easily at reasonable cost because, to provide high quality and avoid certain artifacts, very high-picture-element density is also required. If a new image were to be written, for example, on the photoreceptor for each print, these requirements for high speed and high density would imply electronic bandwidths and (if laser scanning were used) modulation rates and polygon rotation speeds which are very unlikely to be available at reasonable cost in the foreseeable future. In addition, the difficulties associated with conventional xerographic duplicating and printing include the necessity to repeat the imagewise exposure step continually at high speed.
Xeroprinting is another xerographic printing method. Conceptually, xeroprinting overcomes the above problems in a very simple way. Xeroprinting is an electrostatic printing process for printing multiple copies from a master plate or cylinder. The master plate can comprise a metal sheet upon which is imprinted an image in the form of a thin electrically insulating coating. The master plate can be made by photomechanical methods or by xerographic techniques. From the original, a single xeroprinting "master" can, for example, first be made slowly in, for example, 30 to 60 seconds. This imaged material is typically an electrical conductor with an imagewise pattern of insulating areas made by photomechanical or xerographic techniques; it has different charge acceptance in the imaged and non-imaged areas. Thus, generally, the imaging surface of the master plate comprises an electrically insulating pattern corresponding to the desired image shape and electrically conductive areas corresponding to the background. The xeroprinting master is then uniformly charged; the charge remains trapped only on the insulating areas, and this electrostatic image can then be toned. After toner transfer to paper and possibly cleaning, the charge-tone-transfer-clean process is repeated at high speed. In principle, then, it is possible with a xeroprinting process to retain much of the simplicity, stability and quality of the xerographic process without the need for repeated imagewise exposure. As an additional bonus, it may not be necessary to employ a cleaning step, since the same area is repeatedly toned. Moreover, conventional toners can be used, avoiding the problem of lack of color saturation which is encountered with comparable schemes employing magnetography. High contrast potential and high resolution of the electrostatic latent image are important characteristics that determine print qualities of documents prepared by xeroprinting. However, these prior art xeroprinting techniques can produce prints of inferior quality because an insulating pattern on a metal conductor cannot be fully and uniformly charged near its boundaries. As contrast potential builds up along the boundaries of the insulating pattern, fringing electric fields from the insulating image areas repel incoming ions from the charging device, which is usually a corona charging device, to the adjacent electrically conductive background areas. This results not only in low contrast potential but also in poor print resolution. Additionally, some xeroprinting processes require numerous processing steps and complex equipment to prepare the master and/or final xeroprinted product. Some xeroprinting techniques also require messy photochemical processing and removal of materials in either the image or non-image areas of the master.
In U.S. Pat. No. 3,574,614 (Carreira), a xeroprinting process is disclosed in which the xeroprinting master is formed by applying an electric field to a layer of photoelectrophoretic imaging suspension between a blocking electrode and an injecting electrode, one of which is transparent, the suspension comprising a plurality of photoelectrophoretic particles in an insulating carrier liquid, imagewise exposing the suspension to electromagnetic radiation through the transparent electrode to form complementary images on the surfaces of the electrodes (the light exposed particles migrating from the injecting electrode to the blocking electrode), transferring one of the images to a conductive substrate, uniformly that the binder thickness both within the image formed and the non-image that the binder thickness both within the image formed and the non-image areas ranges from 1 to 20 microns. The xeroprinting process consists of applying a uniform charge to the surface of the image bearing substrate in the presence of electromagnetic radiation to form an electrostatic residual charge pattern corresponding to the non-image areas (areas void of photoelectrophoretic particles), developing the residual charge pattern, transferring the developer from the residual charge pattern to a copy sheet, and repeating the charging, developing and transferring steps. Alternatively, the insulating binder can be intimately blended with the dispersion of the photoelectrophoretic particles prior to insertion of the liquid mixture between the electrodes. The areas from which photoelectrophoretic particles have migrated become insulating and capable of supporting an electrostatic charge. A major problem, however, is that insulating images supported directly on a conducting substrate cannot be charged close to the edges, because fringe fields drive incoming ions to the grounded substrate. Another disadvantage of these processes is that they require the use of a liquid photoelectrophoretic imaging suspension to prepare the master. Additionally, the master making processes are extremely complicated, entailing the removal of one of the electrodes, transfer of one of the complementary images to a conductive substrate, and application of an organic insulating binder to the conductive substrate. Such complicated master making processes are inconvenient to the user and can adversely affect the print quality. They also require additional time to dry the image prior to use as a xeroprinting master.
Unlike the liquid photoelectrophoretic imaging suspension system described in U.S. Pat. No. 3,574,614, solid imaging members have been prepared for dry migration systems. Dry migration imaging members are well known, and are described in detail in, for example, U.S. Pat. No. 3,975,195 (Goffe), U.S. Pat. No. 3,909,262 (Goffe et al.), U.S. Pat. No. 4,536,457 (Tam), U.S. Pat. No. 4,536,458 (Ng), U.S. Pat. No. 4,013,462 (Goffe et al.), and "Migration Imaging Mechanisms, Exploitation, and Future Prospects of Unique Photographic Technologies, XDM and AMEN", P. S. Vincett, G. J. Kovacs, M. C. Tam, A. L. Pundsack, and P. H. Soden, Journal of Imaging Science 30 (4) July/August, pp. 183-191 (1986), the disclosures of each of which are totally incorporated herein by reference Migration imaging members containing charge transport materials in the softenable layer are also known, and are disclosed, for example, in U.S. Pat. Nos. 4,536,457 (Tam) and 4,536,458 (Ng). In a typical embodiment of these migration imaging systems, a migration imaging member comprising a substrate, a layer of softenable material, and photosensitive marking material is imaged by first forming a latent image by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation such as light. Where the photosensitive marking material is originally in the form of a fracturable layer contiguous with the upper surface of the softenable layer, the marking particles in the exposed area of the member migrate in depth toward the substrate when the member is developed by softening the softenable layer.
The expression "softenable" as used herein is intended to mean any material which can be rendered more permeable, thereby enabling particles to migrate through its bulk. Conventionally, changing the permeability of such material or reducing its resistance to migration of migration marking material is accomplished by dissolving, swelling, melting, or softening, by techniques, for example, such as contacting with heat, vapors, partial solvents, solvent vapors, solvents, and combinations thereof, or by otherwise reducing the viscosity of the softenable material by any suitable means.
The expression "fracturable" layer or material as used herein means any layer or material which is capable of breaking up during development, thereby permitting portions of the layer to migrate toward the substrate or to be otherwise removed. The fracturable layer is preferably particulate in the various embodiments of the migration imaging members. Such fracturable layers of marking material are typically contiguous to the surface of the softenable layer spaced apart from the substrate, and such fracturable layers can be substantially or wholly embedded in the softenable layer in various embodiments of the imaging members.
The expression "contiguous" as used herein is intended to mean in actual contact, touching, also, near, though not in contact, and adjoining, and is intended to describe generically the relationship of the fracturable layer of marking material in the softenable layer with the surface of the softenable layer spaced apart from the substrate.
The expression "optically sign-retained" as used herein is intended to mean that the dark (higher optical density) and light (lower optical density) areas of the visible image formed on the migration imaging member correspond to the dark and light areas of the illuminating electromagnetic radiation pattern.
The expression "optically sign-reversed" as used herein is intended to mean that the dark areas of the image formed on the migration imaging member correspond to the light areas of the illuminating electromagnetic radiation pattern and the light areas of the image formed on the migration imaging member correspond to the dark areas of the illuminating electromagnetic radiation pattern.
The expression "optical contrast density" as used herein is intended to mean the difference between maximum optical density (D.sub.max) and minimum optical density (D.sub.min) of an image. Optical density is measured for the purpose of this invention by diffuse densitometers with a blue Wratten No. 94 filter. The expression "optical density" as used herein is intended to mean "transmission optical density" and is represented by the formula: EQU D=log.sub.10 [l.sub.o /l]
where l is the transmitted light intensity and l.sub.o is the incident light intensity. For the purpose of this invention, all values of transmission optical density given in this invention include the substrate density of about 0.2 which is the typical density of a metallized polyester substrate.
There are various other systems for forming such images, wherein non-photosensitive or inert marking materials are arranged in the aforementioned fracturable layers, or dispersed throughout the softenable layer, as described in the aforementioned patents, which also discloses a variety of methods which can be used to form latent images upon migration imaging members.
Various means for developing the latent images can be used for migration imaging systems. These development methods include solvent wash away, solvent vapor softening, heat softening, and combinations of these methods, as well as any other method which changes the resistance of the softenable material to the migration of particulate marking material through the softenable layer to allow imagewise migration of the particles in depth toward the substrate. In the solvent wash away or meniscus development method, the migration marking material in the light struck region migrates toward the substrate through the softenable layer, which is softened and dissolved, and repacks into a more or less monolayer configuration. In migration imaging films supported by transparent substrates alone, this region exhibits a maximum optical density which can be as high as the initial optical density of the unprocessed film. On the other hand, the migration marking material in the unexposed region is substantially washed away and this region exhibits a minimum optical density which is essentially the optical density of the substrate alone. Therefore, the image sense of the developed image is optically sign-reversed. Various methods and materials and combinations thereof have previously been used to fix such unfixed migration images. In the heat or vapor softening developing modes, the migration marking material in the light struck region disperses in the depth of the softenable layer after development and this region exhibits D.sub.min which is typically in the range of 0.6 to 0.7. This relatively high D.sub.min is a direct consequence of the depthwise dispersion of the otherwise unchanged migration marking material. On the other hand, the migration marking material in the unexposed region does not migrate and substantially remains in the original configuration, i.e. a monolayer. In migration imaging films supported by transparent substrates, this region exhibits a maximum optical density (D.sub.max) of about 1.8 to 1.9. Therefore, the image sense of the heat or vapor developed images is optically sign-retained.
Techniques have been devised to permit optically sign-reversed imaging with vapor development, but these techniques are generally complex and require critically controlled processing conditions. An example of such techniques can be found in U.S. Pat. No. 3,795,512, the disclosure of which is totally incorporated herein by reference.
For many imaging applications, it is desirable to produce negative images from a positive original or positive images from a negative original (optically sign-reversing imaging), preferably with low minimum optical density. Although the meniscus or solvent wash away development method produces optically sign-reversed images with low minimum optical density, it entails removal of materials from the migration imaging member, leaving the migration image largely or totally unprotected from abrasion. Although various methods and materials have previously been used to overcoat such unfixed migration images, the post-development overcoating step can be impractically costly and inconvenient for the end users. Additionally, disposal of the effluents washed from the migration imaging member during development can also be very costly.
The background portions of an imaged member can sometimes be transparentized by means of an agglomeration and coalescence effect. In this system, an imaging member comprising a softenable layer containing a fracturable layer of electrically photosensitive migration marking material is imaged in one process mode by electrostatically charging the member, exposing the member to an imagewise pattern of activating electromagnetic radiation, and softening the softenable layer by exposure for a few seconds to a solvent vapor thereby causing a selective migration in depth of the migration material in the softenable layer in the areas which were previously exposed to the activating radiation. The vapor developed image is then subjected to a heating step. Since the exposed particles gain a substantial net charge (typically 85 to 90 percent of the deposited surface charge) as a result of light exposure, they migrate substantially in depth in the softenable layer towards the substrate when exposed to a solvent vapor, thus causing a drastic reduction in optical density. The optical density in this region is typically in the region of 0.7 to 0.9 (including the substrate density of about 0.2) after vapor exposure, compared with an initial value of 1.8 to 1.9 (including the substrate density of about 0.2). In the unexposed region, the surface charge becomes discharged due to vapor exposure. The subsequent heating step causes the unmigrated, uncharged migration material in unexposed areas to agglomerate or flocculate, often accompanied by coalescence of the marking material particles, thereby resulting in a migration image of very low minimum optical density (in the unexposed areas) in the 0.25 to 0.35 range. Thus, the contrast density of the final image is typically in the range of 0.35 to 0.65. Alternatively, the migration image can be formed by heat followed by exposure to solvent vapors and a second heating step which also results in a migration image with very low minimum optical density. In this imaging system as well as in the previously described heat or vapor development techniques, the softenable layer remains substantially intact after development, with the image being self-fixed because the marking material particles are trapped within the softenable layer.
The word "agglomeration" as used herein is defined as the coming together and adhering of previously substantially separate particles, without the loss of identity of the particles.
The word "coalescence" as used herein is defined as the fusing together of such particles into larger units, usually accompanied by a change of shape of the coalesced particles towards a shape of lower energy, such as a sphere.
Generally, the softenable layer of migration imaging members is characterized by sensitivity to abrasion and foreign contaminants. Since a fracturable layer is located at or close to the surface of the softenable layer, abrasion can readily remove some of the fracturable layer during either manufacturing or use of the imaging member and adversely affect the final image. Foreign contamination such as fingerprints can also cause defects to appear in any final image. Moreover, the softenable layer tends to cause blocking of migration imaging members when multiple members are stacked or when the migration imaging material is wound into rolls for storage or transportation. Blocking is the adhesion of adjacent objects to each other. Blocking usually results in damage to the objects when they are separated.
The sensitivity to abrasion and foreign contaminants can be reduced by forming an overcoating such as the overcoatings described in U.S. Pat. No. 3,909,262, the disclosure of which is totally incorporated herein by reference. However, because the migration imaging mechanisms for each development method are different and because they depend critically on the electrical properties of the surface of the softenable layer and on the complex interplay of the various electrical processes involving charge injection from the surface, charge transport through the softenable layer, charge capture by the photosensitive particles and charge ejection from the photosensitive particles, and the like, application of an overcoat to the softenable layer can cause changes in the delicate balance of these processes and result in degraded photographic characteristics compared with the non-overcoated migration imaging member. Notably, the photographic contrast density can degraded. Recently, improvements in migration imaging members and processes for forming images on these migration imaging members have been achieved. These improved migration imaging members and processes are described in U.S. Pat. No. 4,536,458 (Ng) and U.S. Pat. No. 4,536,457 (Tam).
U.S. Pat. No. 3,574,614 (Carreira) discloses a process in which a layer of photoelectrophoretic imaging suspension is subjected to an applied electric field between a blocking electrode and an injecting electrode, one of which is transparent, the suspension comprising a plurality of photoelectrophoretic particles in an insulating carrier liquid, imagewise exposing the suspension to electromagnetic radiation through the transparent electrode to form complementary images on the surfaces of the electrodes (the light exposed particles migrating from the injecting electrode to the blocking electrode), transferring one of the images to a conductive substrate, uniformly applying to the image bearing substrate an organic insulating binder such that the binder thickness both within the image formed and the non-image areas ranges from 1 to 20 micrometers, applying a uniform charge to the surface of the image bearing substrate in the presence of electromagnetic radiation to form an electrostatic residual charge pattern corresponding to the non-image areas (areas void of photoelectrophoretic particles), developing the residual charge pattern, transferring the developer from the residual charge pattern to a copy sheet and repeating the charging, developing and transferring steps. Alternatively, the insulating binder can be intimately blended with the dispersion of the photoelectrophoretic particles prior to insertion of the liquid mixture between the electrodes. The areas from which photoelectrophoretic particles have migrated become insulating and capable of supporting an electrostatic charge.
U.S. Pat. No. 4,536,458 (Ng) discloses a migration imaging member comprising a substrate and an electrically insulating softenable layer on the substrate, the softenable layer comprising migration marking material located at least at or near the surface of the softenable layer spaced from the substrate, and a charge transport molecule. The migration imaging member is electrostatically charged, exposed to activating radiation in an imagewise pattern, and developed by decreasing the resistance to migration, by exposure either to solvent vapor or heat, of marking material in depth in the softenable layer at least sufficient to allow migration of marking material whereby marking material migrates toward the substrate in image configuration. The preferred thickness of the softenable layer is about 0.7 to 2.5 micrometers, although thinner and thicker layers can also be utilized.
U.S. Pat. No. 4,536,457 (Tam) discloses a process in which a migration imaging member comprising a substrate and an electrically insulating softenable layer on the substrate, the softenable layer comprising migration marking material located at least at or near the surface of the softenable layer spaced from the substrate, and a charge transport molecule (e.g. the imaging member described in U.S. Pat. No. 4,536,458) is uniformly charged and exposed to activating radiation in an imagewise pattern. The resistance to migration of marking material in the softenable layer is thereafter decreased sufficiently by the application of solvent vapor to allow the light exposed particles to retain a slight net charge to prevent agglomeration and coalescence and to allow slight migration in depth of marking material towards the substrate in image configuration, and the resistance to migration of marking material in the softenable layer is further decreased sufficiently by heating to allow non-exposed marking material to agglomerate and coalesce. The preferred thickness is about 0.5 to 2.5 micrometers, although thinner and thicker layers can be utilized.
U.S. Pat. No. 4,880,715 (Tam et al.), the disclosure of which is totally incorporated by reference, discloses a xeroprinting process wherein the xeroprinting master is a developed migration imaging member wherein a charge transport material is present in the softenable layer and non-exposed marking material in the softenable layer is caused to agglomerate and coalesce. According to the teachings of this patent, the xeroprinting process entails uniformly charging the master to a polarity the same as the polarity of charges which the charge transport material is capable of transporting, followed by flood exposure of the master to form a latent image, development of the latent image with a toner, and transfer of the developed image to a receiving member. The contrast voltage of the electrostatic latent image obtainable from this process generally initially increases with increasing flood exposure light intensity, typically reaches a maximum value of about 60 percent of the initially applied voltage and then decreases with further increase in flood exposure light intensity. The light intensity for the flood exposure step thus generally must be well controlled to maximize the contrast potential.
U.S. Pat. No. 4,883,731 (Tam et al.), the disclosure of which is totally incorporated herein by reference, discloses an imaging system in which an imaging member comprising a substrate and an electrically insulating softenable layer on the substrate, the softenable layer comprising migration marking material locked at least at or near the surface of the softenable layer spaced from the substrate, and a charge transport material in the softenable layer is imaged by electrostatically charging the member, exposing the member to activating radiation in an imagewise pattern, and decreasing the resistance to migration of marking material in the softenable layer sufficiently to allow the migration marking material struck by activating radiation to migrate substantially in depth towards the substrate in image configuration. The imaged member can be used as a xeroprinting master in a xeroprinting process comprising uniformly charging the master to a polarity the same as the polarity of charges which the charge transport material is capable of transporting, uniformly exposing the charged master to activating illumination to form an electrostatic latent image, developing the latent image to form a toner image, and transferring the toner image to a receiving member. A charge transport spacing layer comprising a film forming binder and a charge transport compound may be employed between the substrate and the softenable layer to increase the contrast potential associated with the surface changes of the latent image. The contrast voltage of the electrostatic latent image obtainable from this process generally initially increases with increasing flood exposure light intensity, reaches a maximum value of about 50 percent of the initially applied voltage and then decreases with further increase in flood exposure light intensity. The light intensity for the flood exposure step thus generally must be well controlled to maximize the contrast potential.
U.S. Pat. No. 4,853,307 (Tam et al.), the disclosure of which is totally incorporated herein by reference, discloses a migration imaging member containing a copolymer of styrene and ethyl acrylate in at least one layer adjacent to the substrate. When developed, the imaging member can be used as a xeroprinting master. According to the teachings of this patent, the xeroprinting process entails uniformly charging the master to a polarity the same as the polarity of charges which the charge transport material is capable of transporting, followed by flood exposure of the master to form a latent image, development of the latent image with a toner, and transfer of the developed image to a receiving member.
U.S. Pat. No. 4,970,130 (Tam et al.), the disclosure of which is totally incorporated herein by reference, discloses a xeroprinting process which comprises (1) providing a xeroprinting master comprising (a) a substrate and (b) a softenable layer comprising a softenable material, a charge transport material capable of transporting charges of one polarity and migration marking material situated contiguous to the surface of the softenable layer spaced from the substrate, wherein a portion of the migration marking material has migrated through the softenable layer toward the substrate in imagewise fashion; (2) uniformly charging the xeroprinting master to a polarity opposite to the polarity of the charges that the charge transport material in the softenable layer is capable of transporting; (3) uniformly exposing the charged master to activating radiation, thereby discharging those areas of the master wherein the migration marking material has migrated toward the substrate and forming an electrostatic latent image; (4) developing the electrostatic latent image; and (5) transferring the developed image to a receiver sheet. The process results in greatly enhanced contrast potentials or contrast voltages between the charged and uncharged areas of the master subsequent to exposure to activating radiation, and the charged master can be developed with either liquid developers or dry developers. The contrast voltage of the electrostatic latent image obtainable from this process generally initially increases with increasing flood exposure light intensity, typically reaches a plateau value of about 90 percent of the initially applied voltage even with further increase in flood exposure light intensity.
While these known imaging members and printing processes are suitable for printing fixed data, a need remains for simultaneous printing of fixed data with variable data.
One prior art technique for printing fixed data and variable data is to print the fixed data first (typically consisting of high resolution images) using an offset press and subsequently to print the variable data (typically consisting of simple low resolution images) with a xerographic laser printer. Because offset printing is a time-consuming and expensive process, it becomes necessary to produce a large quantity of prints of fixed data only (for example, pre-printed business forms) in one printing run to reduce the cost; the variable data are printed later as needed in a xerographic laser printer. This process results in increased inventory cost and waste if changes in fixed data are required. Another disadvantage of this process is that the technique requires printing to be carried out using different printing engines and different imaging members, which makes maintaining accurate registration of the variable data and fixed data difficult.
Another prior art approach to printing fixed data and variable data is to use laser xerography to print both the fixed data and the variable data is to use laser xerography to print both the fixed data the variable data simultaneously. Since the photoreceptor must be laser-scanned once for each print, however, high speed printing at high resolution requires the use of massive memory and high data transfer rate and is thus a very expensive process. A trade-off between resolution and throughput speed becomes necessary.
The most desirable approach would be to use the same imaging member or process for printing both the fixed data and the variable data and to combine the advantages of a master-based printing system for printing the fixed data high resolution images and the advantages of a photoreceptor-based printing system for printing the lower resolution variable data. Since the fixed data high resolution images need to be written only once to yield a printing master, high resolution high speed printing could be obtained at much lower cost.
U.S. Pat. No. 4,835,570 (Robson), the disclosure of which is totally incorporated herein by reference, discloses an apparatus in which fixed and variable indicia are printed on a receiving member. One portion of a xeroprinting master has an imagewise pattern corresponding to the fixed indicia formed thereon. The xeroprinting master is uniformly charged and the portion thereof having the imagewise pattern formed thereon is uniformly exposed to light energy, which records a fixed electrostatic latent image corresponding to the fixed indicia thereon. Another portion of the charged xeroprinting master is selectively exposed to light energy to record a variable electrostatic latent image corresponding to the variable indicia thereon. The fixed and variable electrostatic latent images are developed, and the developed image is transferred to the receiving member to print the fixed and variable indicia thereon. The xeroprinting master can be a migration imaging member comprising, for example, a substrate (which may be conductive), an optional charge transport spacing layer, and a layer of softenable material containing a fracturable layer of migration marking material contiguous with the upper surface of the softenable layer. The master is uniformly charged by a corona generating device. Thereafter, the uniformly charged master is imagewise exposed to activating illumination. The light exposed xeroprinting master is then exposed to solvent vapor. Heat energy is then applied to the solvent treated xeroprinting master and the process for forming the electrostatic latent image thereon is completed. The xeromaster is made according to the process disclosed in U.S. Ser. No. 07/140,860 (U.S. Pat. No. 4,880,715). However, there are several disadvantages of this xeromaster when it is used for printing fixed and variable data, including the undersirable treatment with the vapor of a flammable organic solvent for master-making. Additionally, during the xeroprinting process, the charged xeromaster is selectively discharged (in non-imaged areas) to record the variable data. The electrostatic contrast voltage for the variable data is about 85-90 percent of the initially applied voltage. If the xeromaster is initially charged to 800 volts, the contrast voltage for the variable data is about 680-720 volts. On the other hand, the maximum electrostatic contrast voltage for the fixed data is about 60 percent of the initially applied voltage. Thus, the contrast voltage for the fixed data image is about 480 volts. The significantly different contrast voltages for the fixed data and variable data can cause non-uniform xerographic development and therefore non-uniform printing.
U.S. Pat. No. 4,124,286 (Barasch) discloses a method and apparatus for xerographically printing a composite record based on first and second complementary sources of information. The first source of information is imaged onto a photoconductive medium having the property of persistent conductivity to form a conductive image representative thereof. The conductive image is then transferred onto a second photoconductive medium in the form of a latent electrostatic image. The second, complementary source of information is imaged onto the second photoconductive medium, preferably by a scanning laser, as an overlay on the image of the first source. The composite electrostatic image so formed is then developed by the application of toner material and transferred onto a record medium.
U.S. Pat. No. 4,167,324 (Wu) discloses an apparatus for xerographically printing a composite record based on fixed and variable data. A first source of information is imaged onto a photoconductive drum to form a first electrostatic image thereof. The second, complementary source of information may be derived from a central processing unit in signal form. The signals received from the CPU are used to modulate the output beam of a scanning laser. The modulated laser output beam is directed to a stylus belt positioned in close surface proximity to the photoconductive drum bearing the first electrostatic image. The stylus belt includes an electrically conductive layer and a photoconductive layer, and is responsive to the incident laser energy to translate it into a corresponding charge pattern. This charge pattern is overlaid on the first electrostatic image to form a composite electrostatic image. The composite image is then developed and transferred onto a record medium in a conventional manner.
While known imaging members and processes are suitable for their intended purposes, a need remains for improved processes which allow simultaneous printing of fixed and variable data using the same imaging member and the same printing engine, thus avoiding the problem of mis-registration of the variable data relative to the fixed data. A need also remains for improved processes that allow simultaneous printing of fixed data and variable data at high speed, high resolution and low cost. Further, there is a need for processes for simultaneously printing fixed data and variable data by a xeroprinting method employing heat development of the master, wherein no flammable volatile organic solvents are required. Heat development generally is preferred to vapor or solvent development for reasons of ease of implementation in a machine/office environment, speed, cost, simplicity, and solvent containment and recovery difficulties. There is also a need for processes for simultaneously printing fixed data and variable data by a xeroprinting method, wherein the fixed data areas and the variable data areas of the xeromaster exhibit substantially similar electrostatic contrast voltages or contrast potentials. Additionally, there is a need for processes for simultaneously printing fixed data and variable data by a xeroprinting method wherein high electrostatic contrast voltages or contrast potentials of over 90 percent of charge acceptance are obtained on the xeromaster. In addition, a need remains for processes for simultaneously printing fixed data and variable data that result in uniformly high quality images.